[SI-LIST] Re: 答复: 答复:答复: HDMI Frequency Failing RE Test by 7dB!!!!
- From: "Kenneth W. Egan" <kegan@xxxxxxxxxxxxx>
- To: "zhenwwan@xxxxxxxxx" <zhenwwan@xxxxxxxxx>
- Date: Thu, 24 May 2012 21:37:55 -0500
In HMDI, there are 4 macro symbols that help minimize CDR drift. These macro
symbols are the typically case the majority of issues of EMI in HDMI signaling,
due to their periodic nature, occurring exactly every horizontal and vertical
sync times.
These symbols are basically 1010101011, and variants thereof, and are NOT
randomized.
HDMI is NOT a fully DC balanced code, thought its similar to 8b10b, it only has
an average DC balance per horizontal line.
KWE
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On May 24, 2012, at 8:36 PM, "Zhenwei Wang (zhenwwan)" <zhenwwan@xxxxxxxxx>
wrote:
> Hi Boris,
> Could you please tell me how to calculate this issue? It must be
> interesting.
>
>
>
> BR
>
> Zhenwei(Jason) Wang
>
> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>
>
>
> ������: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
> ����ʱ��: 2012��5��24�� 18:22
> �ռ���: Zhenwei Wang (zhenwwan); Long Yang
> ����: ah.vinod@xxxxxxxxx; SI-LIST
> ����: RE: [SI-LIST] ��: ��: HDMI Frequency Failing RE Test by 7dB!!!!
>
>
>
> Dear Zhenwei Wang,
>
>
>
> By calculations it can be concluded that intra-pair skew of a differential
> pseudo random bit stream will only result in a low level wide band EMI
> without spectral lines.
>
>
>
> In case of non equal rise and fall times this will lead to spectral lines
> that are 6 dB lower for PRBS compared to clock.
>
>
>
> Kind regards
>
> Boris Traa
>
> System design engineer EMC
>
>
>
> It's the currents that make circuits work or fail.
>
>
>
> Philips Innovation Services/EMC center
>
> Room 2.020
>
> High Tech Campus 26
>
> 5656AE Eindhoven, The Netherlands
>
> Tel: ++ 31 40 27 43766
>
> Fax: ++ 31 40 27 42224
>
> E-mail: boris.traa@xxxxxxxxxxx <mailto:boris.traa@xxxxxxxxxxx>
>
>
>
> From: Zhenwei Wang (zhenwwan) [mailto:zhenwwan@xxxxxxxxx]
> Sent: Thursday 24 May 2012 11:49 AM
> To: Long Yang
> Cc: Traa, Boris; ah.vinod@xxxxxxxxx; SI-LIST
> Subject: ��: [SI-LIST] ��: ��: HDMI Frequency Failing RE Test by 7dB!!!!
>
>
>
> If the intra-pair skew is too much bigger, the cross-point of Data+ and
> Data- will not stand on the virtual ground. Then DC return current will flow
> through a ground line. You know every line has inductance. So the noise can
> be get with equation V=Lx(did/dot). The power of return current could be
> radiate through long cable.
>
> Maybe the reason I said was not the dominant part. We needs
> information to deny it.
>
>
>
> BR
>
> Zhenwei(Jason) Wang
>
> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>
>
>
> ������: Long Yang [mailto:long.0.yang@xxxxxxxxx]
> ����ʱ��: 2012��5��24�� 17:38
> �ռ���: Zhenwei Wang (zhenwwan)
> ����: Traa, Boris; ah.vinod@xxxxxxxxx; SI-LIST
> ����: Re: [SI-LIST] ��: ��: HDMI Frequency Failing RE Test by 7dB!!!!
>
>
>
> Skew should be related to stand-wave antenna resonance.
>
> On Thu, May 24, 2012 at 2:11 AM, Zhenwei Wang (zhenwwan) <zhenwwan@xxxxxxxxx>
> wrote:
>
> Hi Boris,
> Actually, I am just guessing. EMI issue has three key features:
> Aggressor, Coupling trace and Receiver. Based Vine's description, the HDMI
> cable acted as the coupling trace in his design. But when the same cable
> connected Sony Blue ray disc and TV, the radiation disappear(Vend did not say
> that directly). So I guessed that in one or two or three TMDS differential
> pair, some shielding line worked as the antenna to radiate the bit clock
> frequency.
> BTW, if have a HDMI SI report(especially intra-pair skew or cross-point
> of TMDS), the guessing will be clear. I know the feeling when EMC test
> failed, much more pressure. So good luck to Vend.
>
> BR
> Zhenwei(Jason) Wang
> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>
>
> -----�ʼ�ԭ��-----
>
> ������: Traa, Boris [mailto:boris.traa@xxxxxxxxxxx]
> ����ʱ��: 2012��5��24�� 16:34
> �ռ���: Zhenwei Wang (zhenwwan); ah.vinod@xxxxxxxxx; SI-LIST
> ����: RE: [SI-LIST] ��: HDMI Frequency Failing RE Test by 7dB!!!!
>
>
> Dear Zhenwei Wang,
>
> Assuming the data is pseudo random, do you think that inter and intra pair
> skew will cause clock related spectral lines. I'm would think that EMI will
> look like wide band noise. Only in case of different rise and fall times for
> intra pair signals spectral lines may appear.
>
> Kind regards
> Boris Traa
> System design engineer EMC
>
> It's the currents that make circuits work or fail.
>
> Philips Innovation Services/EMC center
> Room 2.020
> High Tech Campus 26
> 5656AE Eindhoven, The Netherlands
> Tel: ++ 31 40 27 43766 <tel:%2B%2B%2031%2040%2027%2043766>
> Fax: ++ 31 40 27 42224 <tel:%2B%2B%2031%2040%2027%2042224>
> E-mail: boris.traa@xxxxxxxxxxx
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Zhenwei Wang (zhenwwan)
> Sent: Thursday 24 May 2012 4:05 AM
> To: ah.vinod@xxxxxxxxx; SI-LIST
> Subject: [SI-LIST] ��: HDMI Frequency Failing RE Test by 7dB!!!!
>
> Hi Vinod,
> I went through the email about your issue. Yes, if the pixel clock is
> 74.25Mhz, the data rate is ten times of pixel clock, equal 742.5Mhz.
> Conceptually, TMDS signal have a virtual AC ground. So there is no DC current
> requirement through ground pin. My suggestion: you should check the parameter
> "inter pair skew" of each differential data line.
>
> BR
> Zhenwei(Jason) Wang
> Cisco Systems (Shanghai) Video Technology Co., Ltd.
>
>
> -----�ʼ�ԭ��-----
> ������: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> ��� vinod ah
> ����ʱ��: 2012��5��23�� 21:58
> �ռ���: SI-LIST
> ����: [SI-LIST] HDMI Frequency Failing RE Test by 7dB!!!!
>
> Hi All,
>
> I am designing a board with HDMI input and HDMI output. I am facing EMI issue
> at 742.5MHz (failing FCC limits by 7dB) when running 1080p30 on both Input
> and output HDMI i.e. BLu ray player connected to HDMI input connector of my
> board is giving out data at 1080p30 and HDMI out of my board is connected to
> TV which is also 1080p30 content. So i am unable to find out how is 742.5MHz
> coming out as radiation as it is 10th Harmonic of pixel clock
> 74.25MHz!!!!!!!. I am not facing any issues with other harmonics except for
> this. So i am totally confused on how to go about debugging this issue.
>
> Note: All the signals are routed on top layer without vias and all signals
> have solid ground plane reference. The blu ray player and TV used, is tested
> for radiation and no significant levels seen.
>
> Regards
> Vinod A H
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